Tuning fork driver



y 1951 A. N. STANTON 2,558,991

TUNING FORK DRIVER Filed Dec. 5, 1949 FIG. 2 FIG. 4

INVENTOR.

WWW,

Patented July 3, 1951 UNITED STATES PATENT OFFICE 7 Claims.

This invention relates to tuning forks and more particularly to driving means for tuning forks.

In many applications the energy available to drive a tuning fork is very small at the time of initiation of operation, which is the time during which the energy need of the driving means is greatest. It is therefore necessary that the energy available be utilized with apt efficiency. Furthermore, the driving means must be compact, and light in weight in order that its use be practicable in applications where weight and size are limiting factors.

Accordingly, it is an object of my invention to provide a new and improved driving means for tuning forks.

It is another object of my invention to provide a new and improved electromagnetic driving means for tuning forks.

It is another object of my invention to provide a new and improved electromagnetic driving means for a tuning fork which applies the driving force over a considerable area of the tuning fork.

It is another object of my invention to provide a new and improved electromagnetic driving means for a tuning fork which allows minimum clearance between the tines of the tuning fork and the pole pieces of the driving means.

It is another object of my invention to provide a new and improved electromagnetic driving means for a tuning fork which applies symmetrical driving forces to the tines of the tuning fork with the use of only one driving coil.

It is still another object of my invention to provide a new and improved electromagnetic driving means for mechanical vibrators which will cause the frequency of vibration of the Vibrator to be equal to the frequency of the exciting alternating current in the driving means.

Briefly stated, my new and improved driving means for tuning forks comprises a tubular main portion of magnetic material provided at each end with a pole piece of magnetic material. Each pole piece is provided with a pair of spaced substantially circular apertures, the apertures of axis of the tubular portion is disposed within the.

A driving coil main tubular portion and between the pole pieces. The tuning fork to be driven is disposed within the substantially circular apertures, each tine ly ing within two aligned apertures of the pole pieces and having its inner side substantially in line with the side edges of the tongues which form part of the sides of the aligned circular apertures. The driving coil may be energized by either a pulsating direct current or an alternating current to cause the tines of the tuning fork to move alternately into positions adjacent each other between the inwardly projecting tongues of the pole pieces and into positions remote from each other and beyond the inwardly projecting tongues of the pole pieces.

For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawing in which:

Figure 1 is a top plan view of a preferred embodiment of my invention;

Figure 2 is a sectional view taken along line 22 of Figure 1;

Figure 3 is a top plan view of a modified form of the device shown in Figures 1 and 2;

Figure 4 is a top plan view of another modified form of the device shown in Figures 1 and 2.

Referring now to the accompanying drawing, Figures 1 and 2 illustrate a preferred embodiment of tuning fork driving means 9 which comprises a tubular member ID. Tubular member [0 may be made of a magnetic substance having a low reluctance, such as soft iron, or it may be a permanent magnet which is magnetized parallel to its main axis. Positioned at each end of tubular member I!) perpendicular to the main axis of tubular member iii are disk shaped pole pieces II and I2. Pole pieces H and [2 are preferably made to have a diameter equal to the inside diameter of tubular member i8 and are positioned within tubular member it having their outside surfaces flush with the ends of tubular member It). It will be obvious that pole pieces II and I2 may be made to have a diameter equal to the outside diameter of tubular member. In this case, the pole pieces I l and i2 would be positioned at each end of tubular member I!) and would have their outside periphery coinciding with the outer periphery of tubular member Ill. The construction illustrated in the drawing is preferred however, since the pole pieces I l and [2 can be easily secured to tubular member if! by providing a tight fit between the inner cylindrical surface of tubular member [Bend the outer annular surfacesofdisks H and I2! apertures hi and 15 of pole piece it is a substantially rectangular passage which is formed by the inwardly projecting tongue portions l9 and 2% Pole piece i2 is an exact duplicate of pole piece H. Further description and illustration of pole piece i2 is therefore unnecessary.

The fork 2i to be driven by driving means d has tines 22 and 23 which are disposed in apertures i i and iii, and i5 and ii, respectively. The inner sides of tines 22 and 23 are aligned on each side of tongue members it and 2&3 so that a slight inward movement of tines 22 and 23 toward each other will bring them directly between the tongue members it and 2c of pole pieces It and 2. The tines 22 and 23 are driven toward each other by the magnetic field set up by coil it when coil is is energized. If we assume now that tubular member it is of soft iron and that coil i3 is so energized that pole piece it is a north pole and pole piece it is a south pole of the driving means 9, the flux flowing through tongue members 59 and 26 will seek the flux path of lowest reluctance to the tongue members i9 and 20 (not shown) of pole piece i2. Since tuning fork ii is made of magnetic material, the flux will travel from tongue member 29 of pole piece i i through tines 22 and 23 to tongue member is of pole piece 52. Similarly, flux flowing from tongue member 25 of pole piece M will travel through tines 22 and 23 to its corresponding tongue member 28 (not shown) of pole piece B2. The magnetic field set up by coil it between the tongue members 59 and 2c of pole piece i i and tongue members it and 25) (not shown) of pole piece 42 will exert a force on tines 22 and 23 which will draw tines 22 and 23 toward each other. When the current in coil is ceases to flow, the force drawing tines 22 and 23 together is removed and tines 22 and 23 move away from each other and their momentum will carry them past their original positions to a position remote from each other. If another pulse of current is applied to coil l3 as tines 22 and 23 as they return from the positions remote to each other in their original positions, tines 22 and 23 will again be drawn to positions near each other. By properly timing the pulses of unidirectional current transmitted to coil l3, tuning fork 2! can be set and maintained in vibration at a frequency equal to the frequency of pulsation of the unidirec tional current in coil 5%. Pole pieces ii and i2 will always be north and south magnetic poles, respectively, as long as the direction of flow of current in coil i3 is not changed.

If alternating current is supplied to coil it, and tubular member it and pole pieces ii and 62 are of soft iron, then the tuning fork 25 will vibrate a frequency which is twice the frequency of the alternating current. Tines 22 and 23 will be drawn toward each other twice during each cycle of the alternating current since each half cycle of the alternating current will set up a separate or opposite magnetic flux between pole pieces H and i2. For example, during the posihating current.

tive half cycle of current pole piece If may be a north pole and pole piece 52 will then be a south pole. During this half cycle tines 22 and will be first toward each other and will then move back to positions remote from each other. During the negative half cycle of current, pole piece it will become a south pole and pole piece it will become a north pole. During this negative half cycle, tines 22 and 23 will again be drawn toward each other and will move back to positions remote from each other. In this manner two equal and opposite fluxes will be set up in driving means 9 during each cycle of the alternating current flowing in coil 63 and conse quently tines 22 and 23 will also be drawn toward each other twice during each cycle of the alterin this manner, the frequency of vibration of tuning fork it caused by driving means 9 will be twice the frequency of the alternating current flowing in coil it.

In many applications, it is desirable that the tuning fork vibrate at a frequency equal to the frequency of the alternating current applied to coil it In order to make the frequency of vibration of tuning fork 25 equal to the frequency of the alternating current flowing in coil 53, the tubular member it is permanently magnetized parallel to its main axis. In this case, tubular member it is made of a suitable magnetic alloy piece i 5 having a high magnetic retentivity. Pole pieces ii and ii are made of soft iron in all cases. If we assume now that tubular member it is a permagnet, tines 22 and it will be constantly drawn toward other but the strength of the permanent magnet, which tubular member iii constitutes, and the position of tir es 22 and 23 with respect to tongue members 59 and 2c of pole pieces 5 i and 5.: are so chosen that tin-es 22 and 23 may be drawn still closer together when a current is supplied to coil it which strengthens the magnetic flux between pole pieces ii and 62. For example assuming that the magnetization of tubular member iii is such that pole is a north pole and pole piece 92 is a south pole, and that a positive half cycle of alternating current in coil it will also tend to make pole piece ii a north pole and pole piece i2 a south pole, a positive half cycle of alterhating current flowing in. coil it will cause tines 22 and 23 to be drawn still closer to each other. The succeeding negative half cycle of alternating current in coil it will tend to cause pole piece it to become a south pole and pole piece 02 to become a north pole. The strength of the tubular member iii permanent magnet, and the number of turns in, and the current transmitted by, coil i 3 are such however, that the negative half cycle of current can never reverse the polarity of pole pieces ii and E2. The negative half cycle of current will merely lessen the amount of flux between pole pieces ii and 52, decrease the force drawing tines 222 and 23 toward each other, and therefore allow tines 22 and 23 to move further away from each other. The next P cycle of alternating current will again draw tines 22 and 23 toward each other and again allow them to move into positions relatively remote from each way. In this way each cycle of alter nating current in coil iii will cause one cycle 5 of vibration equal to the frequency of the alternating current.

Since the tines 22 and 23, as shown in Figure 1, move transversely with respect to tongue members i9 and 23, a very small air gap between tongue members l9 and 20 and tines 22 and 23 may be employed. The probability of tines 22 and 23 hitting or contacting any portion of driving means 9 is minimized since a very large clearance for normal and abnormal vibration is provided by apertures l4, l5, l6 and I1. Vibration of tines 22 and 23 in directions perpendicular to the normal directions of vibration will be very small even under external physical impacts to fork 2! since the rigidity of tines 22 and 23 is comparatively great in the direction perpendicular to the normal direction of vibration of fork 2|.

The forces exerted on tines 22 and 23 by the flux flowing between pole pieces H and i2 are symmetrical once fork 2i is properly positioned in driving means 9 since only one coil [3 is employed. Where two coils are employed, one to drive each tine 22 and 23, considerable time and care must be employed to so position each coil with respect to its tine that the forces exerted on the tines of the fork are equal. In addition, the coils must be identical and must be supplied with equal energizing currents. The driving means 9 constructed in accordance with the teachings of my invention are simply and inexpensively constructed since only one coil is needed to produce symmetrical driving forces on each tine 22 and 23 of tuning fork 2 1. Moreover, the force exerted on each tine 22 and 23 is applied over a considerable portion of each tine which decreases the amplitude of harmonic vibration of tines 22 and 23. The force exerted on each tine 22 and 23 is applied over the portion of the fork extending from pole piece H to pole piece i2 since the flux flowing from pole piece I l to pole piece i2 through these portions of tines H and i2 will exert forces throughout these portions.

If desired, the tuning fork 2! may be positioned as shown in Figure 3 in which case the movement of tines 22 and 23 will be toward and away from tongue members 19 and 20 instead of transversely between tongue members [9 and 23. The air gaps between tines 22 and 23 and tongue members !9 and 20 will necessarily be greater but the forces applied to tines 22 and 23 will still be symmetrical. The advantages of symmetrical drive by an easily and inexpensively constructed driving means 9 will still remain.

The driving means 3 is preferably positioned intermediate the length of tuning fork 2| so that the magnetic field set up by coil l3 will not set up forces tending to move fork 2| longitudinally parallel to the main axes of tubular member I and coil 13. The pulsating unidirectional current or the alternating current in coil [3 Will tend to generate eddy currents in tubular member ID and pole pieces I! and I2. To avoid excessive heating of these members of driving means 9, tubular member I2 and pole pieces H and [2 are split as at 24 and 25, respectively, to provide air gaps which will prevent the flow of eddy currents about these members. Since the cross sectional areas of tines 22 and 23 are comparatively small, the eddy currents generated in tines 22 and 23 will also be very small and lamination of tines 22 and 23 will usually be unnecessary, the small amount of heat generated in tines 22 and 23 by the eddy currents being easily dissipated into the air in their vibration.

Figure 4 illustrates a modified form of the device illustrated in Figures 1 and 2. In the embodiment illustrated in Figure 4 a central portion 2-5 joining tongue members [9 and 20 is provided on each pole piece II and 12. When coil [3 is energized, the flux flowing between central portions 23 exerts forces on tines 22 and 23 in planes parallel to the plane of vibration of vibrator 2|. Central portions 25 are provided to increase the magnetic forces tending to cause tines 22 and 23 to vibrate.

It will be apparent to those skilled in that art that various changes and modifications may be made in the illustrated and described embodiments of my invention Without departing from the spirit and scope of my invention and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A vibrator comprising a tubular member; a pair of circular pole pieces having diameters equal to the inside diameter of said tubular member, each of said pole pieces being disposed within said tubular member and adjacent one end thereof, each of said pole pieces having an outer surface lying in the same plane normal to the central axis of said tubular member as an adjacent end of said tubular member, said tubular member and said pole pieces being of magnetic material; a tubular coil disposed within said tubular member and between said pole pieces having a central axis coincident with central axis of said tubular member, said pole pieces each being provided with a pair of apertures symmetrically disposed about said central axis and a substantially rectangular aperture communicating with said apertures, the apertures of one of said pole pieces coinciding with the apertures 0f the other of said pole pieces; and a tuning fork having tines extending parallel to said central axis and through said apertures adjacent said substantially rectangular apertures and being adapted to have said tines drawn together and into said substantially rectangular aperture. 7

2. A vibrator comprising a tubular member; a pair of disk shaped pole pieces, one of said pole pieces being disposed at and closing off one end of said tubular member and the other of said pole pieces being disposed at and closing off the other end of said tubular member, each of said pole pieces being provided with an aperture; a pair of tongue members integral with each of said pole pieces and extending inwardly into said aperture and toward each other; a tubular coil disposed Within said tubular member and between said pole pieces; and a tuning fork having tines extending through said apertures of said pole pieces and through said tubular member, said tines being positioned adjacent said tongue members and being adapted to be drawn toward each other and between said tongue members.

3. A vibrator comprising a tubular member; a pair of circular pole pieces, one of said pole pieces being disposed at and closing off one end of said tubular member, the other of said pole pieces being disposed at and closing off the other end of said tubular member, each of said pole pieces being provided with an elongated aperture, each of said pole pieces being provided with a pair of inwardly projecting tongue members; a tubular coil disposed within said tubular member and having a central axis coincident with the central axis of said tubular member; and a fork having a pair of tines disposed within said coil and extending through said elongated apertures of said pole pieces, said tines being disposed adjacent said tongue members and adapted to be drawn toward each other between said tongue members.

4. A vibrator driving means comprising a tubular member syrmnetrically disposed about a central axis; a pair of pole pieces, one of said pole pieces being disposed at and closing off one end of said tubular member and the other of said pole pieces being disposed at and closing oi the other end of said tubular member, each of said pole pieces being provided with an aperture and a pair of tongue members extending inwardly and toward each other constricting said aperture at its central portion; and a tubular coil disposed within said tubular member having a central axis coincident with said central axis of said tubular member, said tubular coil when energized tending to magnetize said tubular member parallel to said central axis, said tubular member and said pole pieces being of magnetic material, said tubular member being permanently magnetized parallel to said central axis.

5. A vibrator driving means comprising a tubular member symmetrically arranged about a cen tral axis; a pair of pole pieces, one of said pole pieces being disposed at and closing off one end of said tubular member and the other of said pole pieces being disposed at and closing on" the other end of said tubular member, each of said pole pieces being provided with a pair of aper tures, each of said pole pieces being provided with a pair of inwardly extending tongue members partially separating said apertures, said apertures and tongue members being symmetrically arranged about said central axis, each of said pole pieces being provided with a central portion conmeeting said tongue members; and a tubular coil within said tubular member having a centrai axis coinciding with said central axis of said tubular member, said coil tending to magnetize said tubular member parallel to said central axis when said coil is energized.

6. A vibrator comprising a tubular member; a pair of pole pieces, one of said pole pieces being disposed at and closing oiT one end of said tubular member, the other of said pole pieces being disposed at and closing off the other end of said tubular member, each of said pole pieces being provided with an elongated aperture, each of said pole pieces being provided with a pair of in wardly projecting tongue members; a tubular coil disposed Within said tubular member and having a central axis coincident with the central axis of said tubular member; and a fork having a pair of tines disposed within said coil and extending through said elongated apertures of said pole pieces, said tines being disposed adjacent said tongue members and adapted to be drawn toward each other between said tongue members.

'7. A vibrator comprising a pair of pole pieces spaced along a central axis and lying in planes normal to said axis; a tubular coil having a central axis coincident with said first mentioned central axis disposed between said pole pieces; means of magnetic material disposed exterior-1y of said coil providing a magnetic connection between said pole pieces, each of said pole pieces being provided with an elongated aperture, each or? said pole pieces being provided with a pair or" inwardly projecting tongue members constricting said aperture, and a fork having a pair of tines disposed within said coil and extending through said apertures of said pole pieces, said tines being disposed adjacent said tongue members and adapted to be drawn toward each other between said tongue members.

AUSTIN N. STANTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,034,200 Carroll July 30, 1912 1,503,987 Demele Aug. 5, 1924 1,560,056 Horton Nov. 3, 1925 2,267,545 VVente Dec. 23, 1941 2,364,656 Price Dec. 12, 1944 

